High Occupancy Vehicle (HOV): Pending HOV Lane Rule Change

High occupancy vehicle (HOV) lanes are designated by a white diamond in the center of the lane and solid white lane lines. They are also referred to as carpool lanes.

What's Set to Change on Sept. 30, 2025? 

There is an pending federal change to high occupancy vehicle (HOV) lane exemptions for alternative fuel vehicles (regulated by 23 U.S.C. 166b).  If Congress does not extend an exemption contained in a 2005 federal law, as of Sept. 30, 2025, alternative fuel vehicles and vehicles with Energy Efficient plates will no longer qualify to use HOV lanes with fewer than two people in the vehicle during restricted times.

What Qualifies as an Alternative Fuel Vehicle? 

An alternative fuel vehicle is one that is powered only by an alternative fuel. State law defines an alternative fuel as one of the following:

• Electric
• Natural gas / CNG or LPG
• Hydrogen
• Blend of 70 percent alternative fuel, 30 percent gasoline (unavailable in Arizona)
• Solar

If a vehicle is converted to operate solely on alternative fuel, the Arizona Department of Environmental Quality must inspect the vehicle and issue an Alternative Fuel Certificate.

Current HOV Lane Privileges

If you have a current alternative fuel vehicle specialty plate, you currently can use the HOV freeway lanes at any time regardless of the number of passengers. HOV lane privileges are authorized by Federal Code 23 U.S.C. 166. 

FAQ

Why is this happening?

The decision on whether to allow this provision in federal code to lapse lies with the federal government. Even though this is a federal matter, ADOT is sharing early word because the outcome affects travelers in the Phoenix area, owners and prospective buyers of alternative fuel vehicles, and businesses selling and servicing alternative fuel vehicles.

Where would this happen?

In Arizona, HOV lanes currently are used on Phoenix-area freeways.

Can anything else affect the ability of alternative fuel vehicles to use HOV lanes? 

Yes. The Federal Highway Administration requires states to produce an annual report identifying degradation of HOV lane traffic flow. HOV lane segments that are out of compliance with traffic flow requirements must receive further analysis and countermeasures designed to improve travel time. If a segment that allows low-emission or energy efficient vehicles, which includes alternative fuel vehicles, remains out of compliance, federal code [23 USC 166(d)(2)] requires local authorities to take actions that can include limiting or discontinuing use by those vehicles during restricted times. 

Where can I learn more about HOV lanes and rules governing them?

ADOT offers a resource at azdot.gov/HOV explaining what HOV lanes are for, who can use them and other topics. It also answers many common questions about HOV lanes.

High Occupancy Vehicle Lanes Degradation Report

The Arizona Department of Transportation (ADOT) Multi-modal Planning Division (MPD) is tasked with updating the High Occupancy Vehicle (HOV) lanes degradation report on an annual basis. The report is provided to the Federal Highway Administration (FHWA) every June 1st and includes 6-months worth of data (October through March). Analysis is performed to identify areas of congestion on the network. Compliance is defined for segments as speeds of 45 mph or faster for 90% of the time over a 180-day period during the weekdays rush hours (excluding holidays) which start from 6 am to 9 am and from 3 pm to 7 pm. Segments that are out of compliance are further analyzed and countermeasures are identified to show continuous improvement in travel time reliability. The HOV lane degradation report details the analysis methods used and the updates in ADOT’s processes, and new initiatives to improve compliance on the roadway network.